Langerhans cells (LC) are the principal antigen presenting cells of the skin, and the outpost of the immune system. Jurgens recently demonstrated that crosslinking FcepsilonRI, the high affinity IgE receptor on LC induces phosphorylation of tyrosine and calcium flux in LC. The phenotypic and functional consequences of crosslinking FcepsiolonRI and LC are unknown, however, a functional role for IgE receptors on LC has been suggested, particularly in atopic dermatitis. The purpose of these studies is to determine the functional significance of high affinity IgE receptors on LC and dendritic cells (DC), and to determine if activation of LC and DC via FcepsilonRI plays a role in the pathogenesis of atopic dermatitis. The specific aims of this proposal are to examine the phenotypic and functional consequences of crosslinking FcepsilonRI on LC an DC and determine if the phenotypic and functional characteristics of LC activated via FcepsilonRI reflect those of LC found in lesions of atopic dermatitis. Normal LC and DC will be activated by crosslinking FcepsilonRIalpha, and activation will be confirmed by demonstrating phosphorylation of tyrosine residue and calcium flux following receptor crosslinking. The phenotype of activated LC and DC will be determined by multicolor flow cytometry. Functional consequences of activation will be determined by measuring the magnitude as well as the type of T cell response (Th1 vs Th2), generated by the presentation of antigen to T cells by activated LC or DC. The type of T cell response will be determined by flow cytometry for intracellular cytokine production and will be correlated to cytokine secretion as determined by ELISA. Clinical studies will compare the phenotypic and functional characteristics of LC and DC from atopic and normal subjects, and determine if activated LC or DC are henotypically and functionally similar to LC or DC from atopic donors. Once a functional role for high affinity IgE receptors on LC and DC is established, later studies will focus on the mechanisms of signal transduction via FcepsilonRI itself, and clinical studies will seek to develop therapeutic strategies to treat atopic dermatitis by inhibiting the activation of LC and DC via FcepsilonRI. Through these studies, the candidate will gain new expertise in the fields of signal transduction, molecular biology and allergy, which along with her current expertise in dermatology and cellular immunology will facilitate her long term goals to study the immunologic mechanisms of atopic dermatitis.